1. Field of the Invention
The present invention generally relates to fuel-injected outboard motors. More particularly, the present invention relates to a fuel system venting arrangement for such outboard motors.
2. Description of the Related Art
Outboard motors are used to power marine vehicles. The outboard motors typically include an engine positioned within a protective cowling of the outboard motor. The outboard motor is attached to the back of the watercraft and used to propel the watercraft in a forward or reverse direction. The outboard motors include induction systems and fuel supply systems to provide an air/fuel charge into the combustion chambers for combustion in order to provide a rotary motion to an output shaft that drives the propeller.
In the engines of the outboard motors, fuel is often supplied to a vapor separator upstream of a fuel injector. The vapor separator is used to remove vapors from the fuel prior to the fuel being pumped into a fuel rail associated with the fuel injectors by a high pressure fuel pump. This separation reduces entrainment of gases and vapors within the fuel supply, which can cause problems with the fuel injection system. Separated fuel vapor and air typically is discharged from the vapor separator through a discharge duct into the induction system for combustion with the air/fuel charge. Typically, the vent air and fuel vapor that is discharged from the vapor separator tank is delivered through an intake pipe together with air flowing from a plenum chamber.
The vent air or fuel vapor that is discharged from the vapor separator generally comprises a portion of evaporated gasoline and therefore is flammable. As more vent air flows into a single combustion chamber, the output power of the associated cylinder increases because of the overly rich air fuel mixture. Conversely, as the level of this vent vapor decreases in a single cylinder, the power of that cylinder decreases due to a lean mixture.
As is known, the plenum chamber generally contains a large volume of air. The vent air coming into this large volume of air from the vapor separator generally is not equally mixed with the air. Under such conditions, the proportion of vent vapor to intake air delivered to each individual cylinder from the plenum chamber fluctuates. The fluctuation in proportion from cylinder to cylinder causes unstable engine performance and reduces engine power. In particular, in multiple cylinder engines, the inconsistent vent air proportion delivered to each combustion chamber creates a disparity in output power between cylinders.
Accordingly, it is desired to have a fuel supply system and induction system that can supply a substantially equal and subdivided portion of the vent vapor to each of the cylinders for combustion. Such an arrangement would lead to more stable engine operation and better overall power output from the engines. In addition, the vent vapor supply should be controllable to increase available power under certain running conditions.
Accordingly, one aspect of the present invention involves an engine comprises a plurality of cylinders that include corresponding combustion chambers. The engine further comprises an induction system and a fuel supply system that are in fluid communication with the combustion chambers. The induction system comprises an intake chamber and a plurality of intake conduits that correspond to the combustion chambers. Each intake conduit is in fluid communication with the intake chamber and the corresponding combustion chamber. A throttle device is positioned between at least one of the intake conduits and the intake chamber to regulate a flow of air into at least one of the combustion chambers. A bypass passage extends from the intake chamber and a portion of the induction system downstream of the throttle device. A flow control member is positioned along the bypass passage to selectively regulate flow through the bypass passage.
In a preferred mode, the fuel supply system comprises a fuel supply. A supply conduit connects the fuel supply to a vapor separation tank. At least one pump is positioned along the supply conduit with a plurality of fuel injectors that are in fluid communication with the vapor separation tank. A vent passage extends between the vapor separation tank and a portion of the bypass passage positioned upstream of the flow control member.
The engine has particular utility in the context of an outboard motor. Thus, in accordance with a further aspect of the present invention, the engine can be provided in an outboard motor with its output shaft arranged in an vertical orientation. A drive shaft of the outboard motor is operatively connected to the output shaft. A transmission selectively couples the drive shaft to a propulsion device of the outboard motor. In this manner, the engine powers the propulsion device which can be driven in multiple operating states by the transmission (e.g., forward or reverse).
Another aspect of the present invention involves a method of controlling flow through a bypass of an induction system. The method comprises sensing an engine operating condition, determining a desired level of bypass flow volume by comparing the engine operating condition to a map of values, and adjusting the bypass flow volume according to a value selected from the map of values by manipulating an bypass flow control member.
Further aspects, features and advantages of the present invention will also become apparent from the detail description of the preferred embodiments that follows.